The long range goal of our research is to develop an effective vaccine against human immunodeficiency virus type-1 (HIV-1) infection. We plan to use avian paramyxoviruses (APMVs) as vectors for delivery of HIV-1 proteins. APMVs do not cause disease in humans and there is no preexisting immunity in humans to APMVs. There are nine serotypes of APMVs, therefore, several serologically distinct vectors can be developed to express different HIV genes for use in prime-boost immunization approach. As a first step towards our goal, we propose here studies to optimize the expression level of HIV-1 envelope glycoprotein (Env), its incorporation into virus particles and the strategy of immunization. We have chosen to use APMV-1, also known as Newcastle disease virus (NDV), because this is the most studied member among APMVs. The results obtained with NDV can be extended to other APMV serotypes in the future. The first objective of our proposal is to identify the optimal 5' and 3' untranslated regions of NDV genes for insertion into HIV Env transcriptional unit to enhance its expression. We will also attempt to enhance the incorporation of HIV Env into NDV envelope by replacement of transmembrane domain and cytoplasmic tail sequences of HIV Env protein with those of NDV F protein individually and collectively. The second objective of our proposal is to evaluate different inoculation routes and prime-boost approaches for eliciting robust systemic and mucosal immune responses in guinea pigs. The optimal strategies will subsequently be moved into monkey studies.